1. Field of the Invention
The present invention relates, in general, to apparatus for measurement of forces and/or moments acting on rotatable members, such as vehicle wheels.
2. Description of the Art
Wheel load transducers are known for attachment to a vehicle wheel to measure torque, moments and forces applied to the wheel. Such transducers, as shown in FIGS. 1 and 2 and described in greater detail hereafter, are typically in the form of an annular member which is affixed at an outer peripheral portion to a rim adapter welded to the wheel rim. The adapter has a plurality of circumferentially spaced apertures which align with corresponding apertures in the outer periphery of the transducer for receiving bolts therethrough to fix to the transducer to the wheel rim.
The transducer includes an inner annular portion which also has a plurality of circumferentially spaced apertures. A hub adapter containing a corresponding circumferential arrangement of apertures is mountable to the inner annular portion and fastened thereto. The hub adapter includes a standard hole arrangement for attachment to a vehicle wheel bolt lugs.
A plurality of radial extending webs or beams interconnect the inner and outer portions of the transducer. Moments and forces exerted on the wheel are measured by sensors, such as strain gages, which are adhesively affixed to exterior surfaces of the webs or beams. Strain gages mounted on the inboard and outboard surfaces of the beams provide torque measurements. Strain gages mounted on the sides of the beams are positioned for providing steering and camber moments and lateral force measurements. This type of transducer is not capable of measuring vertical and fore and aft forces acting on the wheel.
Other more complex transducers are capable of measuring the three directional forces, torque, camber moment and steering moment. However, such wheel load transducers have required many output channels, such as up to twelve output channels to measure the three primary forces and three primary moments or torque exerted on a vehicle wheel.
Thus, it would be desirable to provide a force and/or moment measurement device suitable for use with rotatable members, such as vehicle wheels, which is capable of obtaining force and/or moment measurements with a high degree of accuracy. It would also be desirable to provide such a measurement apparatus which has a minimal number of independent output data channels.
The present invention is in the load transducer for measuring forces on a rotatable member, such as a vehicle wheel.
According to one aspect of the present invention, the load transducer is mountable on a vehicle wheel having a wheel hub and a rim. The load transducer includes a rim adapter mountable to a wheel rim, and a hub adapter mounted to the wheel hub and fixedly connected in force transmission with the rim adapter.
The hub adapter has inner and outer portions.
A plurality of beams extend between the inner and outer portions of the hub adapter. At least one sensor is mounted on each beam for measuring forces exerted on the beam during rotation of the wheel. The beams are disposed substantially parallel to a rotational axis of the wheel and have an inner surface, an outer surface, and interconnecting, opposed side edges.
An outer annular member is connected between the rim adapter and the hub adapter. The outer annular member includes radially spaced inner and outer annular rings. A plurality of circumferentially spaced beams extend between the inner and outer annular rings.
The beams on the hub adapter are preferably oriented substantially perpendicular to the beams on the outer annular member.
In one aspect, an adapter body has an inner wall with a plurality of circumferentially spaced apertures mountable over vehicle wheel lugs. A side wall extends from the inner wall terminating in an outer end, the plurality of beams are circumferentially spaced about the side wall. The beams comprise at least three circumferentially spaced beams. Each beam has a longitudinal axis, with at least one sensor centered on the longitudinal axis.
In another aspect of the invention, the hub adapter includes a wall having a plurality of circumferentially spaced apertures therein mountable over vehicle wheel lugs and fixedly connectable thereto. A side wall extends from the wall and terminates in an outer end.
A separate interior transducer body has first and second ends. A plurality of bores are formed in the first end and alignable with mating bores in the outer end of the hub adapter for receiving fasteners to fixedly connect the interior transducer body to the hub adapter.
A plurality of bores are formed in the second end of the interior transducer body each receiving a fastener for fixedly connecting the interior transducer body in a force transmission arrangement with the rim adapter. A plurality of spaced beams extend between the first and second ends of the interior transducer body. At least one sensor is mounted on each beam for measuring forces exerted on each beam.
The load transducer of the present invention uniquely and economically enables vertical and longitudinal or fore/aft forces to be measured on a rotating member, such as vehicle wheel, by utilizing the existing hub adapter and rim adapter typically employed in vehicle wheel load transducers which include an outer mounted load transducer capable of measuring torque, lateral force and various moments. Beams are uniquely formed in the hub adapter and provide a mounting surface for sensors, such as strain gages, which can be interconnected in a four arm bridge configuration to provide a single output channel corresponding to vertical force and/or longitudinal or fore/aft force.
The hub adapter may be provided as a combined hub adapter and interior load transducer when constructed as a unitary one-piece member. Alternately, the hub adapter may be provided separate from an interior load transducer body and interconnected to the interior load transducer body in a fixed connection. This arrangement enables an identical interior load transducer to be mated with different hub adapters depending upon a vehicle wheel lug bolt pattern and wheel dimensional configuration.
The beams on the hub adapter or interior load transducer body are configured so that the shear strain per unit force is equal in all strain gage locations in a given bridge circuit. This enables the wheel load transducer of the present invention being insensitive to the load path between the rim and hub adapters. The present wheel load transducer also exhibits minimal radial force variation as the wheel rotates to provide more accurate force measurement.